improve [`cast_sign_loss`], to skip warning on always positive expressions
fixes: #11642
changelog: improve [`cast_sign_loss`] to skip warning on always positive expressions
Turns out this is change became quite big, and I still can't cover all the cases, like method calls such as `POSITIVE_NUM.mul(POSITIVE_NUM)`, or `NEGATIVE_NUM.div(NEGATIVE_NUM)`... but well, if I do, I'm scared that this will goes forever, so I stopped, unless it needs to be done, lol.
0e5dc8e630